Universal newborn hearing screening (UNHS) enables early intervention, but the effectiveness of early intervention for improving long-term speech and language outcomes has not been adequately proven. Further, the relative impact of a wide range of factors on short and long-term outcomes remains to be quantified in a prospective manner, and information on the etiology of early- and later-identified children is limited. The study will 1) describe the speech perception, speech production, language, phonological awareness, reading, functional and psycho-social skills in early- and late-identified children who receive amplification prior to 3 years of age over a period of 5 years;2) identify the factors that influence the children's rate of development in different outcome dimensions;3) investigate the etiology of hearing loss for both groups of children;and 4) relate early performance to later outcomes. 400 children will be recruited, half of them newly identified with hearing loss, half who have already received intervention. Within Australia, it is still possible to recruit sufficiently large numbers of early- and late-identified children because some regions have UNHS whereas others do not as yet. Once diagnosed, all children receive the same audiological intervention from the national government service provider. The outcomes of all 400 children will be measured at multiple intervals over five years: 6-, 12-, 24-months post-fitting, and at 3 and 5 years of age. The effect of hearing aid prescription will be studied by randomly assigning newly identified children to receive either the NAL-NL1 or the DSL[i/o] prescription, and the children's performance will be monitored longitudinally. For all 400 children, information related to etiology will be obtained from parents and DMA from neonatal blood spots will be analysed for the presence of cytomegalovirus (CMV) and for the three genetic mutations believed to most commonly cause hearing loss. All outcomes data will be statistically related to a wide range of predictors, and results will be incorporated in a new software tool that will enable clinicians to directly use the many results from this study. Achieving the specific aims will provide the evidence base to 1) guide best-practice intervention and monitoring following diagnosis, and 2) demonstrate the outcomes affected by access to newborn hearing screening and early intervention. The study will be the most comprehensive with regard to predictors, outcomes, representativeness, and number of children.